Solid laminate stringer

ABSTRACT

A solid laminate stringer includes a base segment that forms a first generally trapezoidal cross section. The solid laminate stringer also includes a transition segment abutting the base segment, with concave sides that are continuous with the sides of the base segment. The solid laminate stringer also includes a top segment abutting the transition segment, where the top segment forms a second generally trapezoidal cross section with sides that are continuous with the concave sides of the transition segment. The solid laminate stringer also includes a first overwrap layer covering the top segment, the transition segment, and at least a portion of the base segment. The solid laminate stringer also includes a second overwrap layer overlapping at least a portion of the first overwrap layer covering the base segment.

FIELD

The present disclosure generally relates to solid laminate stringers foruse in an aircraft structure, and methods for fabricating solid laminatestringers.

BACKGROUND

Solid laminate stringers, such as those formed from carbon fiberreinforced polymer, are commonly used as part of a structural system foraircraft components. For example, a series of stringers may be laminatedto the inner skin of an aircraft wing or hull. The structural system maybe designed to withstand delamination of the stringers from the innerskin of the aircraft components and thermal cracking of the stringers asthe aircraft components are subjected to a combination of aerodynamicloads and temperature changes over time.

What is needed is an improved solid laminate stringer with increaseddelamination strength and improved resistance to thermal cracking.

SUMMARY

In one example, a solid laminate stringer for use in an aircraft isdescribed, including a base segment having a first plurality of plies ofreinforcement material, where the base segment forms a first generallytrapezoidal cross section with sides having a first slope angle withrespect to a first stacked ply of the base segment. The solid laminatestringer also includes a transition segment abutting the base segment,the transition segment having a second plurality of plies ofreinforcement material, where the transition segment forms a crosssection having concave sides that are continuous with the sides of thebase segment. The solid laminate stringer also includes a top segmentabutting the transition segment, the top segment having a thirdplurality of plies of reinforcement material, where the top segmentforms a second generally trapezoidal cross section with sides that arecontinuous with the concave sides of the transition segment, and wherethe sides have a second slope angle with respect to the first stackedply of the base segment that is greater than the first slope angle. Thesolid laminate stringer also includes a first overwrap layer having atleast one ply of reinforcement material, where the first overwrap layercovers the top segment, the transition segment, and at least a portionof the base segment. The solid laminate stringer also includes a secondoverwrap layer having at least one ply of reinforcement material, wherethe second overwrap layer overlaps at least a portion of the firstoverwrap layer covering the base segment.

In another example, a method for fabricating a solid laminate stringerof a structural system is described. The method includes laying up abase segment of the stringer onto a surface, where laying up the basesegment includes stacking a first plurality of plies of reinforcementmaterial such that the base segment forms a first generally trapezoidalcross section with sides having a first slope angle with respect to thesurface. The method also includes laying up a transition segment of thestringer abutting the base segment, where laying up the transitionsegment includes stacking a second plurality of plies of reinforcementmaterial such that the transition segment forms a cross section havingconcave sides that are continuous with the sides of the base segment.The method also includes laying up a top segment of the stringerabutting the transition segment, where laying up the top segmentincludes stacking a third plurality of plies of reinforcement materialsuch that the top segment forms a second generally trapezoidal crosssection that is continuous with the transition segment, with sideshaving a second slope angle with respect to the surface that is greaterthan the first slope angle. The method also includes laying up a firstoverwrap layer, where laying up the first overwrap layer includesstacking at least one ply of reinforcement material over the topsegment, the transition segment, and at least a portion of the basesegment. The method also includes laying up a second overwrap layer,where laying up the second overwrap layer includes stacking at least oneply of reinforcement material such that the second overwrap layeroverlaps at least a portion of the first overwrap layer covering thebase segment, and such that the second overwrap layer covers at least aportion of the surface adjacent to the base segment. The method alsoincludes simultaneously curing the base segment, the transition segment,the top segment, the first overwrap layer, and the second overwraplayer.

In another example, a structural system is described including alaminate skin of an aircraft component, where the laminate skin includesan inner surface. The structural system also includes a solid laminatestringer positioned on the inner surface of the laminate skin. The solidlaminate stringer includes a base segment including a first plurality ofplies of reinforcement material, where the base segment forms a firstgenerally trapezoidal cross section with sides having a first slopeangle with respect to the inner surface of the laminate skin. The solidlaminate stringer also includes a transition segment abutting the basesegment, the transition segment including a second plurality of plies ofreinforcement material, where the transition segment forms a crosssection having concave sides that are continuous with the sides of thebase segment. The solid laminate stringer also includes a top segmentabutting the transition segment, the top segment including a thirdplurality of plies of reinforcement material, where the top segmentforms a second generally trapezoidal cross section with sides that arecontinuous with the concave sides of the transition segment, where thesides have a second slope angle with respect to the inner surface of thelaminate skin that is greater than the first slope angle. The solidlaminate stringer also includes a first overwrap layer including atleast one ply of reinforcement material, where the first overwrap layercovers the top segment, the transition segment, and at least a portionof the base segment. The solid laminate stringer also includes a secondoverwrap layer including at least one ply of reinforcement material,where the second overwrap layer overlaps at least a portion of the firstoverwrap layer covering the base segment, and where the second overwraplayer further covers at least a portion of the inner surface of thelaminate skin adjacent to the base segment.

The features, functions, and advantages that have been discussed can beachieved independently in various examples or may be combined in yetother examples, further details of which can be seen with reference tothe following description and drawings.

BRIEF DESCRIPTION OF THE FIGURES

The novel features believed characteristic of the illustrative examplesare set forth in the appended claims. The illustrative examples,however, as well as a preferred mode of use, further objectives anddescriptions thereof, will best be understood by reference to thefollowing detailed description of an illustrative example of the presentdisclosure when read in conjunction with the accompanying Figures.

FIG. 1 illustrates a perspective view of a solid laminate stringer,according to an example implementation.

FIG. 2 illustrates a close up view of a solid laminate stringer,according to an example implementation.

FIG. 3 illustrates a cross-sectional plan view of a base segment of asolid laminate stringer, according to an example implementation.

FIG. 4 illustrates a cross-sectional plan view of a transition segmentof a solid laminate stringer, according to an example implementation.

FIG. 5 illustrates a cross-sectional plan view of a top segment of asolid laminate stringer, according to an example implementation.

FIG. 6 illustrates a cross-sectional plan view of a second overwraplayer of a solid laminate stringer, according to an exampleimplementation.

FIG. 7 illustrates a line of symmetry through a solid laminate stringer,according to an example implementation.

FIG. 8 illustrates a cross-sectional plan view of a cap charge of asolid laminate stringer, according to an example implementation.

FIG. 9 illustrates a schematic view of a plurality of terminating pliesin a runout portion of a solid laminate stringer, according to anexample implementation.

FIG. 10 illustrates a perspective view of a runout portion of a solidlaminate stringer, according to an example implementation.

FIG. 11 illustrates a cross-sectional view of a runout portion of asolid laminate stringer, according to an example implementation.

FIG. 12 illustrates an elastic center of gravity of a solid laminatestringer, according to an example implementation.

FIG. 13 illustrates an elastic center of gravity of a runout portion ofa solid laminate stringer, according to an example implementation.

FIG. 14 shows a flowchart of an example method for fabricating a solidlaminate stringer of a structural system, according to an exampleimplementation.

DETAILED DESCRIPTION

Disclosed examples will now be described more fully with reference tothe accompanying Figures, in which some, but not all of the disclosedexamples are shown. Indeed, several different examples may be describedand should not be construed as limited to the examples set forth herein.Rather, these examples are described so that this disclosure will bethorough and complete and will fully convey the scope of the disclosureto those skilled in the art.

Examples discussed herein include solid laminate stringers and methodsfor fabricating solid laminate stringers. The stringers may include aseries of segments including stacked plies of reinforcing material in aconfiguration that increases delamination strength and resistance tothermal cracking. The stringers may also include a configuration thatfacilitates stringer runout, and may reduce local strain or stress inthe structural system that includes the stringers.

By the term “about” or “substantial” and “substantially” or“approximately,” with reference to amounts or measurement values, it ismeant that the recited characteristic, parameter, or value need not beachieved exactly. Rather, deviations or variations, including, forexample, tolerances, measurement error, measurement accuracylimitations, and other factors known to those skilled in the art, mayoccur in amounts that do not preclude the effect that the characteristicwas intended to provide.

Referring now to FIGS. 1 and 2, FIG. 1 shows a perspective view of asolid laminate stringer 100, according to an example implementation.Similarly, FIG. 2 shows a close up view of a solid laminate stringer100, according to an example implementation. For instance, the stringer100 may be used as a reinforcing member on the interior laminate skin ofan aircraft component, such as the hull or wing. To improve delaminationstrength, the stringer 100 may be laid up in a series of segments thatgradually change in stiffness through a variable fiber concentration inthe axial direction of the stringer 100. For instance, as shown in FIG.1, the stringer 100 may include a base segment 101.

The base segment 101 forms a first generally trapezoidal cross section.For instance, the topmost and bottommost plies in the base segment 101,as shown in FIGS. 1 and 2, may be substantially parallel. The basesegment 101 further includes sides 103 having a first slope angle 104with respect to a first stacked ply 105, i.e. the bottommost ply, ofreinforcement material of the base segment 101. For instance, the firststacked ply 105 may contact the inner surface 702 of the laminate skin701 of the aircraft component, and may form the bottom of the stringer100 as shown in FIG. 1. Consecutively stacked plies of the base segment101 may be slightly narrower in width than the first stacked ply 105,resulting in the trapezoidal cross section of base segment 101.

In some implementations, the first slope angle 104 of the base segment101 may be within a range of between about 10 to 20 degrees. Forinstance, the first slope angle 104, for both sides 103 of the stringer100, may be 15 degrees. This may allow the base segment 101 to be flaredout wider than the remainder of the stringer 100, which may provide alarger unit area to bear the delamination stresses that may act betweenthe laminate skin 701 and base segment 101, thereby reducing thedelamination stresses.

The stringer 100 may further include a transition segment 201 abuttingthe base segment 101. As shown in FIG. 1, the transition segment 201 ispositioned atop the base segment 101. The transition segment 201 forms across section having concave sides 203 that are continuous with thesides 103 of the base segment 101. In some implementations, the concavesides 203 of the transition segment 201 may include one or more arcshaving a radius of at least about 0.25 inches, which may provide acontinuous transition from the sides 103 of the base segment 101 tosides 303 of a top segment 301.

Accordingly, the stringer 100 may include a top segment 301 abutting thetransition segment 201. As shown in FIG. 1, the top segment 301 sitsatop the transition segment 201 and forms a second generally trapezoidalcross section with sides 303 that are continuous with the concave sides203 of the transition segment 201. The sides 303 have a second slopeangle 304 with respect to the first stacked ply 105 of the base segment101. The second slope angle 304 is greater than the first slope angle104, as seen in FIG. 1. In some implementations, the second slope angle304 may be within a range of between about 60 to 75 degrees. Forinstance, the second slope angle 304, for both sides 303 of the stringer100, may be 70 degrees.

In some embodiments, the top segment 301 may include a top surface 305that joins each side 303 of the top segment 301 at a convex arc 306,which may reduce the likelihood of thermal cracking near or at the uppercorners of the stringer 100 in some situations, as discussed below.

The stringer may further include a first overwrap layer 401. The firstoverwrap layer 401 may cover the top segment 301, the transition segment201, and at least a portion of the base segment 101. For example, in theexample shown in FIGS. 1 and 2, the first overwrap layer 401 extendsfrom a first end 403 to a second end 404, and covers the full width ofthe base segment 101 on both sides of the stringer 100.

As mentioned above, the convex arc 306 may provide a smooth transitionbetween the sides 303 and a top surface 305 of the top segment 301,which transition is then duplicated in the first overwrap layer 401. Forexample, the convex arc 306 of the top segment 301 may have a radius ofat least about 0.15 inches. This may allow tensile stresses in topsegment 301 close to the first overwrap layer 401 may to be moreeffectively distributed over the convex arc 306. Conversely, a laminatestringer with a sharper transition between the sides and top mayexperience heighted tensile stresses at this location, which may lead tocracking of the stringer 100.

In some implementations, the stringer 100 may also include a secondoverwrap layer 501. The second overwrap layer 501 may overlap at least aportion of the first overwrap layer 401 covering the base segment 101.As can be seen in FIG. 2, the second overwrap layer 501 covers a portionof the first overwrap layer 401, as a first end 503 of the secondoverwrap layer 501 extends to the top of the transition segment 201, asshown in FIG. 1. Alternatively, the first end 503 of the second overwraplayer 501 may taper to an end at approximately the middle of thetransition segment 201, as shown in FIG. 2.

The second overwrap layer 501 may also cover a portion of laminate skin701. Further, because the second overwrap layer 501 is not continuousover the stringer 100, the two sides 103 of the base segment 101 may becovered by two different sections of the second overwrap layer 501. Ascan be seen in FIG. 1, a second end of the second overwrap layer 501extends to approximately the top of the transition segment 201.

As noted above, the stringer 100 may be laid up in a series of segmentsthat, from the base segment 101 to the top segment 301, graduallyincrease in stiffness. Because the laminate skin 701 generally has alower stiffness that the stringer 100, this arrangement allows the basesegment 101 to have stiffness that is closer to that of the laminateskin 701, which may be beneficial. For instance, a difference in thematerial properties of two adjacent laminate components, such as thelaminate skin 701 and the base segment 101, may lead to heightenedinterlaminate tensile stresses, and may contribute to delamination ofthe stringer 100 from the laminate skin 701 is some cases. The same mayresult from a difference in the coefficient of thermal expansion (CTE)between adjacent laminate components. Moreover, in the configurationdiscussed, an increased stiffness may still be provided in the topsegment 301, where the greatest resistance to bending is derived.

The stiffness of the segments in the stringer 100 may be graduallyincreased by varying, in the respective plies of each segment oroverwrap layer, the fiber concentration in the axial direction 601 ofthe stringer 100. A traditional layup of the stringer 100 may includeplies of reinforcing material positioned at angles to the axialdirection 601 of the stringer 100 including 0 degrees, 45 degrees, −45degrees and 90 degrees. The number of plies among each of these anglesin a traditional layup may be evenly distributed, for instance. However,the current examples contemplate non-traditional layups with pliesarranged at several different angles that affect the fiber concentrationin the axial direction 601, as well as traditional 0/45/−45/90 layupsthat include an uneven distribution of plies, favoring those arranged inthe axial direction 601 (i.e. 0 degree plies).

For example, as shown in FIG. 1, the first overwrap layer 401 mayinclude at least one ply of reinforcement material 402 that is arrangedwith respect to an axial direction 601 of the stringer 100 at one ormore angles within ranges of between about 15 to 25 degrees and betweenabout −15 to −25 degrees. For instance, the at least one ply ofreinforcement material 402 may include two plies of tape plies arrangedat 20 degrees and −20 degrees, respectively, the orientations of whichcan be seen in FIG. 1. This may result in reducing a mismatch betweenthe CTE of the first overwrap layer 401 as compared to that of the topsegment 301, as the plies are arranged relatively close to the axialdirection 601 of the stringer 100, or 0 degrees. These properties mayapproach the orientation of the top segment 301 (discussed below), whichmay also reduce interlaminate tensile stresses within and between thetop segment 301 and the first overwrap layer 401.

Similarly, the base segment 101 includes a first plurality of plies ofreinforcement material 102, which can be seen in the cross-sectionalplan view of the base segment 101 shown in FIG. 3. The first pluralityof plies of reinforcement material 102 may include plies arranged withrespect to the axial direction 601 of the stringer 100 in a traditionallayup, at angles including 0 degrees, 45 degrees, −45 degrees and 90degrees. However, about 38% to 44% of the first plurality of plies ofreinforcement material 102 are arranged at 0 degrees, or parallel to theaxial direction 601 of the stringer 100. For instance, 40% of the pliesin the first plurality of plies of reinforcement material 102 may be 0degree plies. This may provide an aggregate stiffness of the basesegment 101 that is greater than that of the laminate skin 701, but notso much greater that undesired interlaminate tensile stresses areintroduced.

Further, the transition segment 201 includes a second plurality of pliesof reinforcement material 202, an example of which can be seen in thecross-sectional plan view of the transition segment 201 shown in FIG. 4.For instance, the second plurality of plies of reinforcement material202 may include plies arranged in a non-traditional layup, arranged withrespect to the axial direction 601 of the stringer 100 at angles withinranges of between about 25 to 35 degrees and between about −25 to −35degrees. In some implementations, for instance, the second plurality ofplies of reinforcement material 202 may be arranged at 30 degrees and−30 degrees, as in FIG. 4. This arrangement may provide a greaterstiffness in the transition segment 201 than the arrangement of the basesegment 101 discussed above, due to a greater resulting fiberconcentration in the axial direction 601.

Alternatively, the second plurality of plies of reinforcement material202 may include plies arranged in a traditional 0/45/−45/90 degreelayup, but with about 42% to 48% of the second plurality of plies ofreinforcement material 202 arranged at 0 degrees. For instance, 45% ofthe plies in the second plurality of plies of reinforcement material 202may be 0 degree plies. Again, this may provide a greater stiffness inthe transition segment 201 than the arrangement of the base segment 101discussed above, but a stiffness that is less than that of the topsegment 301, discussed below.

The top segment 301 includes a third plurality of plies of reinforcementmaterial 302, an example of which can be seen in the cross-sectionalplan view of the top segment 301 shown in FIG. 5. For example, the thirdplurality of plies of reinforcement material 302 may include pliesarranged in a non-traditional layup with respect to the axial direction601 of the stringer 100 at angles within ranges of between about 20 to35 degrees and between about −20 to −35 degrees. In someimplementations, for instance, the third plurality of plies ofreinforcement material 302 may be arranged at 22 degrees and −22degrees, as in FIG. 5. This may provide a greater stiffness in the topsegment 301 than either arrangement of the transition segment 201discussed above, due to a greater resulting fiber concentration in theaxial direction 601.

Alternatively, the third plurality of plies of reinforcement material302 may include plies arranged in a non-traditional layup with respectto the axial direction 601 of the stringer 100 at a combination ofangles including 10 degrees, −10 degrees, 60 degrees, and −60 degrees.Again, this may result in a greater fiber concentration in the axialdirection 601 than the options discussed for the transition segment 201above.

As yet another example, the third plurality of plies of reinforcementmaterial 302 may include plies arranged in a traditional 0/45/−45/90degree layup, but with about 45% to 60% of the third plurality of pliesof reinforcement material 302 arranged at 0 degrees. For instance, 55%of the plies in the third plurality of plies of reinforcement material302 may be 0 degree plies, a greater proportion than discussed for thetransition segment 201 above, resulting in a greater stiffness of thetop segment 301.

The second overwrap layer 501 includes at least one ply of reinforcementmaterial 502, an example of which can be seen in the cross-sectionalplan view of the second overwrap layer shown in FIG. 6. For instance, atleast one ply of reinforcement material 502 may include two plies offabric arranged at −45 degrees and 45 degrees respectively, as in FIG.6.

Referring now to FIG. 7, in some implementations, the top segment 301 ofthe solid laminate stringer 100 may further include a cap charge 307abutting the third plurality of plies of reinforcement material 302. Forexample, the cap charge 307 may be positioned atop the top surface 305of the top segment 301, as in FIG. 7. Further, the cap charge 307includes a fourth plurality of plies of reinforcement material 308,which may be arranged with respect to the axial direction 601 of thestringer 100 at angles that are substantially the same as the angles ofthe first plurality of plies of reinforcement material 102. For example,as can be seen in FIG. 8, the fourth plurality of plies of reinforcementmaterial 308 are arranged at the same 0/45/−45/90 degree angles as thefirst plurality of plies of reinforcement material 102 in the basesegment 101, shown in FIG. 3. Moreover, the distribution of pliesbetween the traditional layup angles may be substantially the same asthe base segment 101 as well. For instance, like the base segment 101,40% of the plies in the fourth plurality of plies of reinforcementmaterial 308 may be 0 degree plies.

In this arrangement of the stringer 100, where the cap charge 307mirrors the base segment 101, the arrangement of the first, second,third and fourth plurality of plies with respect to the axial direction601 of the stringer 100 may be approximately symmetric about a line ofsymmetry 602 between the base segment 101 and the cap charge 307, asshown in FIG. 7. The symmetry may be approximate due to the transitionsegment 201, which does not have a corresponding segment near the top ofthe stringer 100. However, the transition segment 201 may contribute arelatively small portion of the height 604 of the stringer 100, and thusthe deviation from symmetry about the line of symmetry 602 may berelatively small.

The approximately symmetric arrangement of plies in the stringer 100discussed above may be advantageous at the runout ends of the stringer100. For example, it may allow for a plurality of terminating plies 603,located in the middle of the stringer 100, to be successively terminatedin the axial direction 601 of the stringer 100, approximately at theline of symmetry 602, as shown in FIG. 9. For example, as plies areterminated from the middle of the stringer 100, the stringer 100 mayremain approximately symmetric about the line of symmetry 602. Further,each ply in the plurality of terminating plies 603 may be terminated ashorter axial distance from the runout end 605 of the stringer 100,which may reduce the height 604 of the stringer 100 along the axialdirection 601 of the stringer 100. The plies may alternate in beingterminated from just above the line of symmetry 602 to just below theline of symmetry 602, which may help to maintain the approximatesymmetry of the remaining plies.

For purposes of illustrating the stepwise configuration of the pluralityof successive terminating plies 603, the schematic view shown in FIG. 9does not illustrate the remaining plies converging at the line ofsymmetry 602, and thereby reducing the height 604 of the stringer 100.However, this effect can be seen in FIGS. 10 and 11.

FIGS. 10 and 11 show perspective and cross-section views, respectively,of a runout portion of the stringer 100, approaching the runout end 605.As the plurality of terminating plies 603 are terminated from the lineof symmetry 602, as discussed above, the height 604 of the stringer 100is reduced in the direction of the runout end 605. As shown in FIG. 10,the width of the stringer 100 may also increase as the height 604decreases toward the runout end 605. Further, the cap charge 307 and thebase segment 101 remain the uppermost and lowermost plies of thestringer 100, until they are the only plies remaining in the stringer100. Other arrangements are also possible.

Turning now to FIG. 12, a flowchart of a method 800 for fabricating asolid laminate stringer of a structural system is shown, according to anexample implementation. Method 800 shown in FIG. 12 presents an exampleof a method that, for instance, could be used with the stringer 100, asshown in FIGS. 1-11 and discussed above. It should be understood thatfor this and other processes and methods disclosed herein, flowchartsshow functionality and operation of one possible implementation ofpresent examples. In this regard, each block in the flowchart mayrepresent a module, a segment, or a portion of program code, whichincludes one or more instructions executable by a processor forimplementing or causing specific logical functions or steps in theprocess. For example, the method 800 may be implemented by one or morecomputing devices of a robotic assembly system. Alternativeimplementations are included within the scope of the examples of thepresent disclosure, in which functions may be executed out of order fromthat shown or discussed, including substantially concurrently, dependingon the functionality involved, as would be understood by thosereasonably skilled in the art.

At block 802, the method 800 includes laying up a base segment 101 ofthe stringer 100 of a structural system 700 onto a surface 707, as canbe seen with reference to FIGS. 13 and 14. The surface 707 may be, forinstance, the inner surface 702 of the laminate skin 701 of an aircraftcomponent as discussed in the examples above. However, the surface 707could be any other surface suitable for reinforcement by a solidlaminate stringer such as the stringer 100, which may, in combination,form the structural system 700.

As discussed in the examples above, laying up the base segment 101 mayinclude stacking a first plurality of plies of reinforcement material102 such that the base segment 101 forms a first generally trapezoidalcross section with sides 103 having a first slope angle 104 with respectto the surface 707.

In some implementations, laying up the base segment 101 may includestacking the first plurality of plies of reinforcement material 102 suchthat the first slope angle 104 of the base segment 101 is within a rangeof between about 10-15 degrees. Further, laying up the base segment 101may also include arranging the first plurality of plies of reinforcementmaterial 102 with respect to an axial direction 601 of the stringer 100at angles including 0/45/−45/90 degrees. About 38% to 44% of the firstplurality of plies of reinforcement material 102 in the base segment 101may be arranged at 0 degrees, as discussed previously and shown in FIG.3.

At block 804, the method 800 includes laying up a transition segment 201of the stringer 100 abutting the base segment 101, which may includestacking a second plurality of plies of reinforcement material 202 suchthat the transition segment 201 forms a cross section having concavesides 203 that are continuous with the sides 103 of the base segment101, as discussed previously and shown in FIGS. 1 and 2.

Further, laying up the transition segment 201 may include stacking thesecond plurality of plies of reinforcement material 202 such that theconcave sides 203 of the transition segment 201 include one or more arcshaving a radius of at least about 0.25 inches. Laying up the transitionsegment 201 may also include arranging the second plurality of plies ofreinforcement material 202 with respect to an axial direction 601 of thestringer 100 at angles within ranges of between about 25 to 35 degreesand between about −25 to −35 degrees, as discussed above. Alternatively,the second plurality of plies of reinforcement material 202 may bearranged at angles including 0/45/−45/90 degrees, where about 42% to 48%of the second plurality of plies of reinforcement material 202 arearranged at 0 degrees.

At block 806, the method 800 includes laying up a top segment 301 of thestringer 100 abutting the transition segment 201, which may includestacking a third plurality of plies of reinforcement material 302 suchthat the top segment 301 forms a second generally trapezoidal crosssection that is continuous with the transition segment 201. Further, thetop segment may include sides 303 having a second slope angle 304 withrespect to the surface 707 that is greater than the first slope angle104, as discussed previously and as generally shown in FIGS. 1 and 2.

Further, laying up the top segment 301 may include stacking the thirdplurality of plies of reinforcement material 302 such that the secondslope angle 304 of the top segment 301 is within a range of betweenabout 60 to 75 degrees, as noted previously. Laying up the top segment301 may also include arranging the third plurality of plies ofreinforcement material 302 with respect to the axial direction 601 ofthe stringer 100 at angles within ranges of between about 20 to 35degrees and between about −20 to −35 degrees, or at angles including 10degrees, −10 degrees, 60 degrees, and −60 degrees, as contemplated inprevious examples. Further, the third plurality of plies ofreinforcement material 302 may be arranged at angles including0/45/−45/90 degrees, wherein about 45% to 60% of the third plurality ofplies of reinforcement material 302 are arranged at 0 degrees.

At block 808, the method 800 includes laying up a first overwrap layer401, which may include stacking at least one ply of reinforcementmaterial 402 over the top segment 301, the transition segment 201, andat least a portion of the base segment 101.

At block 810, the method 800 includes laying up a second overwrap layer501, which may include stacking at least one ply of reinforcementmaterial 502 such that the second overwrap layer 501 overlaps at least aportion of the first overwrap layer 401 covering the base segment 101,and such that the second overwrap layer 501 covers at least a portion ofthe surface 707 adjacent to the base segment 101, similar to theexamples discussed above.

At block 812, the method 800 includes simultaneously curing the basesegment 101, the transition segment 201, the top segment 301, the firstoverwrap layer 401, and the second overwrap layer 501. In someimplementations, the surface 707 may be an inner surface 702 of alaminate skin 701 of an aircraft, as discussed above. Additionally,before laying up the base segment 101 of the stringer 100, the method800 may involve laying up the laminate skin 701 of the aircraftcomponent. Moreover, simultaneously curing the base segment 101, thetransition segment 201, the top segment 301, the first overwrap layer401, and the second overwrap layer 501 may also include simultaneouslycuring the laminate skin 701 of the aircraft component.

In some implementations, laying up the top segment 301 of the stringer100 of the structural system 700 may include laying up a cap charge 307abutting the third plurality of plies of reinforcement material 302. Asdiscussed above and as shown in FIG. 7-8, laying up the cap charge 307may include stacking a fourth plurality of plies of reinforcementmaterial 308 in an arrangement with respect to the axial direction 601of the stringer 100 that is substantially the same as an arrangement ofthe first plurality of plies of reinforcement material 102 with respectto the axial direction 601 of the stringer 100. As a result, thestructural system 700 may include an arrangement of the first, second,third and fourth plurality of plies with respect to the axial direction601 of the stringer 100 that is approximately symmetric about a line ofsymmetry 602 between the base segment 101 and the cap charge 307, asdiscussed previously.

The method 800 may also include terminating a plurality of terminatingplies 603 in the axial direction 601 of the stringer 100. As noted abovewith respect to FIG. 9, each successive terminating ply may beterminated a shorter axial distance from a runout end 605 of thestringer 100. Further, each terminating ply in the plurality ofterminating plies 603 may be terminated approximately at the line ofsymmetry 602 such that a height 604 of the stringer 100 is reduced alongthe axial direction 601.

In some embodiments, the method 800 may also include increasing athickness 704 of the laminate skin 701 along the axial direction 601 ofthe stringer 100 as the height 604 of the stringer 100 is reduced. Forexample, the structural system 700, including the laminate skin 701 andthe stringer 100, may include an outer mold line 703, which is shown inFIGS. 12-13. The structural system 700 may further include an elasticcenter of gravity 705 that is located a distance 706 from the outer moldline 703 of the laminate skin 701.

FIG. 13 shows an example of the structural system 700, including anindication of the elastic center of gravity 705 where the stringer 100.As plies are terminated from the stringer 100, as discussed above, thereduction in mass may cause the elastic center of gravity 705 to driftdownward, as the distance 706 is reduced. Accordingly, this may causethe bending moment that is resisted along the axial direction 601 of thestringer 100 to act at a different location within the structural system700. This in turn may generate internal loads on the structural system700, which may be undesirable. Consequently, the thickness 704 of thelaminate skin 701 may be increased to offset the reduced height 604 ofthe stringer 100.

However, because the stringer 100 generally has a greater stiffness thanthe laminate skin 701, as discussed above, it may not be possible toincrease the thickness 704 of the laminate skin 701 at a rate sufficientto compensate for the runout of the stringer 100. Therefore, in someembodiments, the method 800 may include laying up structural fillmaterial 708 on the inner surface 702 of the laminate skin 701 andadjacent to the stringer 100 where the height 604 of the stringer 100 isreduced. The structural fill material 708 may balance the runout of thestringer 100 such that the distance 706 from the outer mold line 703 tothe elastic center of gravity 705 is approximately constant along theaxial direction 601 of the stringer 100. In this way, the structuralsystem 700 may minimize internal loads that may be generated if thebending moment acts at a different location for the elastic center ofgravity along different points in the structural system 700.

The description of the different advantageous arrangements has beenpresented for purposes of illustration and description, and is notintended to be exhaustive or limited to the examples in the formdisclosed. Many modifications and variations will be apparent to thoseof ordinary skill in the art. Further, different advantageous examplesmay describe different advantages as compared to other advantageousexamples. The example or examples selected are chosen and described inorder to explain the principles of the examples, the practicalapplication, and to enable others of ordinary skill in the art tounderstand the disclosure for various examples with variousmodifications as are suited to the particular use contemplated

What is claimed is:
 1. A solid laminate stringer for use in an aircraft,the stringer comprising: a base segment comprising a first plurality ofplies of reinforcement material, wherein the base segment forms a firstgenerally trapezoidal cross section with sides having a first slopeangle with respect to a first stacked ply of the base segment; atransition segment abutting the base segment, the transition segmentcomprising a second plurality of plies of reinforcement material,wherein the transition segment forms a cross section having concavesides that are continuous with the sides of the base segment; a topsegment abutting the transition segment, the top segment comprising athird plurality of plies of reinforcement material, wherein the topsegment forms a second generally trapezoidal cross section with sidesthat are continuous with the concave sides of the transition segment,and wherein the sides have a second slope angle with respect to thefirst stacked ply of the base segment that is greater than the firstslope angle; a first overwrap layer comprising at least one ply ofreinforcement material, wherein the first overwrap layer covers the topsegment, the transition segment, and at least a portion of the basesegment; and a second overwrap layer comprising at least one ply ofreinforcement material, wherein the second overwrap layer overlaps atleast a portion of the first overwrap layer covering the base segment.2. The solid laminate stringer of claim 1, wherein the at least one plyof reinforcement material of the first overwrap layer is arranged withrespect to an axial direction of the stringer at one or more angleswithin ranges of between about 15 to 25 degrees and between about −15 to−25 degrees.
 3. The solid laminate stringer of claim 1, wherein the topsegment comprises a top surface that joins each side of the top segmentat a convex arc having a radius of at least about 0.15 inches.
 4. Thesolid laminate stringer of claim 1, wherein the concave sides of thetransition segment comprise one or more arcs having a radius of at leastabout 0.25 inches, and wherein the second plurality of plies ofreinforcement material comprises plies arranged with respect to an axialdirection of the stringer at angles within ranges of between about 25 to35 degrees and between about −25 to −35 degrees, or at angles including0 degrees, 45 degrees, −45 degrees and 90 degrees, wherein about 42% to48% of the second plurality of plies of reinforcement material arearranged at 0 degrees.
 5. The solid laminate stringer of claim 1,wherein the second slope angle of the top segment is within a range ofbetween about 60 to 75 degrees, and wherein the third plurality of pliesof reinforcement material comprises plies arranged with respect to anaxial direction of the stringer at angles within ranges of between about20 to 35 degrees and between about −20 to −35 degrees, or at anglesincluding 10 degrees, −10 degrees, 60 degrees, and −60 degrees, or atangles including 0 degrees, 45 degrees, −45 degrees and 90 degrees,wherein about 45% to 60% of the third plurality of plies ofreinforcement material are arranged at 0 degrees.
 6. The solid laminatestringer of claim 1, wherein the first slope angle of the base segmentis within a range of between about 10 to 20 degrees, and wherein thefirst plurality of plies of reinforcement material comprises pliesarranged with respect to an axial direction of the stringer at anglesincluding 0 degrees, 45 degrees, −45 degrees and 90 degrees, whereinabout 38% to 44% of the first plurality of plies of reinforcementmaterial are arranged at 0 degrees.
 7. The solid laminate stringer ofclaim 6, wherein the top segment further comprises a cap charge abuttingthe third plurality of plies of reinforcement material, wherein the capcharge comprises a fourth plurality of plies of reinforcement material,wherein the fourth plurality of plies of reinforcement material arearranged with respect to the axial direction of the stringer at anglesthat are substantially the same as the angles of the first plurality ofplies of reinforcement material.
 8. The solid laminate stringer of claim7, wherein an arrangement of the first, second, third and fourthplurality of plies with respect to the axial direction of the stringeris approximately symmetric about a line of symmetry between the basesegment and the cap charge, wherein a plurality of terminating plies aresuccessively terminated in the axial direction of the stringer,approximately at the line of symmetry, such that a height of thestringer is reduced along the axial direction of the stringer.
 9. Amethod for fabricating a solid laminate stringer of a structural system,the method comprising: laying up a base segment of the stringer onto asurface, wherein laying up the base segment comprises stacking a firstplurality of plies of reinforcement material such that the base segmentforms a first generally trapezoidal cross section with sides having afirst slope angle with respect to the surface; laying up a transitionsegment of the stringer abutting the base segment, wherein laying up thetransition segment comprises stacking a second plurality of plies ofreinforcement material such that the transition segment forms a crosssection having concave sides that are continuous with the sides of thebase segment; laying up a top segment of the stringer abutting thetransition segment, wherein laying up the top segment comprises stackinga third plurality of plies of reinforcement material such that the topsegment forms a second generally trapezoidal cross section that iscontinuous with the transition segment, with sides having a second slopeangle with respect to the surface that is greater than the first slopeangle; laying up a first overwrap layer, wherein laying up the firstoverwrap layer comprises stacking at least one ply of reinforcementmaterial over the top segment, the transition segment, and at least aportion of the base segment; laying up a second overwrap layer, whereinlaying up the second overwrap layer comprises stacking at least one plyof reinforcement material such that the second overwrap layer overlapsat least a portion of the first overwrap layer covering the basesegment, and such that the second overwrap layer covers at least aportion of the surface adjacent to the base segment; and simultaneouslycuring the base segment, the transition segment, the top segment, thefirst overwrap layer, and the second overwrap layer.
 10. The method ofclaim 9, wherein laying up the transition segment further comprises:stacking the second plurality of plies of reinforcement material suchthat the concave sides of the transition segment comprise one or morearcs having a radius of at least about 0.25 inches; and arranging thesecond plurality of plies of reinforcement material with respect to anaxial direction of the stringer at angles within ranges of between about25 to 35 degrees and between about −25 to −35 degrees, or at anglesincluding 0 degrees, 45 degrees, −45 degrees and 90 degrees, whereinabout 42% to 48% of the second plurality of plies of reinforcementmaterial are arranged at 0 degrees.
 11. The method of claim 9, whereinlaying up the top segment further comprises: stacking the thirdplurality of plies of reinforcement material such that the second slopeangle of the top segment is within a range of between about 60 to 75degrees; and arranging the third plurality of plies of reinforcementmaterial with respect to an axial direction of the stringer at angleswithin ranges of between about 20 to 35 degrees and between about −20 to−35 degrees, or at angles including 10 degrees, −10 degrees, 60 degrees,and −60 degrees, or at angles including 0 degrees, 45 degrees, −45degrees and 90 degrees, wherein about 45% to 60% of the third pluralityof plies of reinforcement material are arranged at 0 degrees.
 12. Themethod of claim 9, wherein laying up the base segment further comprises:stacking the first plurality of plies of reinforcement material suchthat the first slope angle of the base segment is within a range ofbetween about 10 to 20 degrees; and arranging the first plurality ofplies of reinforcement material with respect to an axial direction ofthe stringer at angles including 0 degrees, 45 degrees, −45 degrees and90 degrees, wherein about 38% to 44% of the first plurality of plies ofreinforcement material are arranged at 0 degrees.
 13. The method ofclaim 9, wherein the surface is an inner surface of a laminate skin ofan aircraft component, wherein the method further comprises: beforelaying up the base segment of the stringer, laying up the laminate skinof the aircraft component, wherein simultaneously curing the basesegment, the transition segment, the top segment, the first overwraplayer, and the second overwrap layer further comprises simultaneouslycuring the laminate skin of the aircraft component.
 14. The method ofclaim 13, wherein laying up the top segment of the stringer furthercomprises laying up a cap charge abutting the third plurality of pliesof reinforcement material, wherein laying up the cap charge comprisesstacking a fourth plurality of plies of reinforcement material in anarrangement with respect to an axial direction of the stringer that issubstantially the same as an arrangement of the first plurality of pliesof reinforcement material with respect to the axial direction of thestringer, and such that an arrangement of the first, second, third andfourth plurality of plies with respect to the axial direction of thestringer are approximately symmetric about a line of symmetry betweenthe base segment and the cap charge.
 15. The method of claim 14, furthercomprising: successively terminating a plurality of terminating plies inthe axial direction of the stringer, wherein each successive terminatingply is terminated a shorter axial distance from a runout end of thestringer, and wherein each terminating ply in the plurality ofterminating plies is terminated approximately at the line of symmetrysuch that a height of the stringer is reduced along the axial direction;and increasing a thickness of the laminate skin along the axialdirection of the stringer as the height of the stringer is reduced. 16.The method of claim 15, wherein the laminate skin comprises an outermold line, and wherein the structural system comprises an elastic centerof gravity located a distance from the outer mold line of the laminateskin, and wherein the method further comprises: laying up structuralfill material on the inner surface of the laminate skin and adjacent tothe stringer where the height of the stringer is reduced such that thedistance from the outer mold line to the elastic center of gravity isapproximately constant along the axial direction of the stringer.
 17. Astructural system comprising: a laminate skin of an aircraft component,wherein the laminate skin comprises an inner surface; a solid laminatestringer positioned on the inner surface of the laminate skin, the solidlaminate stringer comprising: a base segment comprising a firstplurality of plies of reinforcement material, wherein the base segmentforms a first generally trapezoidal cross section with sides having afirst slope angle with respect to the inner surface of the laminateskin; a transition segment abutting the base segment, the transitionsegment comprising a second plurality of plies of reinforcementmaterial, wherein the transition segment forms a cross section havingconcave sides that are continuous with the sides of the base segment; atop segment abutting the transition segment, the top segment comprisinga third plurality of plies of reinforcement material, wherein the topsegment forms a second generally trapezoidal cross section with sidesthat are continuous with the concave sides of the transition segment,and wherein the sides have a second slope angle with respect to theinner surface of the laminate skin that is greater than the first slopeangle; a first overwrap layer comprising at least one ply ofreinforcement material, wherein the first overwrap layer covers the topsegment, the transition segment, and at least a portion of the basesegment; and a second overwrap layer comprising at least one ply ofreinforcement material, wherein the second overwrap layer overlaps atleast a portion of the first overwrap layer covering the base segment,and wherein the second overwrap layer further covers at least a portionof the inner surface of the laminate skin adjacent to the base segment.18. The structural system of claim 17, wherein the top segment furthercomprises a cap charge abutting the third plurality of plies ofreinforcement material, wherein the cap charge comprises a fourthplurality of plies of reinforcement material, wherein the fourthplurality of plies of reinforcement material comprises an arrangementwith respect to an axial direction of the stringer that is substantiallythe same as an arrangement of the first plurality of plies ofreinforcement material with respect to the axial direction of thestringer.
 19. The structural system of claim 18, wherein an arrangementof the first, second, third and fourth plurality of plies with respectto the axial direction of the stringer are approximately symmetric abouta line of symmetry between the base segment and the cap charge, whereina plurality of terminating plies are successively terminated in theaxial direction of the stringer, approximately at the line of symmetry,such that a height of the stringer is reduced along the axial directionof the stringer, and wherein a thickness of the laminate skin isconcurrently increased along the axial direction of the stringer. 20.The structural system of claim 19, wherein the laminate skin comprisesan outer mold line, and wherein the structural system comprises anelastic center of gravity located a distance from the outer mold line ofthe laminate skin, and wherein the structural system further comprises:structural fill material positioned on the inner surface of the laminateskin and adjacent to the stringer where the height of the stringer isreduced, such that the distance from the outer mold line to the elasticcenter of gravity is approximately constant along the axial direction ofthe stringer.